Such antennas have already been described, in particular in U.S. Pat. No. 2,158,376, a figure of that patent being reproduced as accompanying FIG. 1.
The antenna is constituted by a sequence of dipoles D1, D2, D3, etc. connected to one another by a system of phase shifters DF1, DF2, etc. More precisely, each dipole D1 is constituted by a cylindrical conductive element 10 and the antenna also comprises two parallel rectilinear conductive elements 12 and 14. The cylindrical conductive elements 10 constituting the dipoles D1, D2, D3 are bonded in alternation to one of the conductors 12 and 14 while surrounding the other conductor. For example, the dipole D1 is constituted by a cylindrical element 10 that is coaxial about conductive element 14 and that is bonded to conductive element 12. The phase shifter elements DF are thus constituted by the same conductive element 12, 14 passing from a position where it is bonded to the cylindrical conductive element to a position where it is disposed on the axis of the following cylindrical conductive element. This change in disposition corresponds substantially to a phase shift of λ/2. Thus, currents flowing in the conductive portions 12 and 14 corresponding to the different dipoles are summed overall. However, the alternating positions of the conductive cylinders about the two conductive rectilinear elements causes the radiation pattern of the antenna assembly to be asymmetrical, and as a result the antenna is not omnidirectional.
Another drawback of the antenna described in the above-cited US patent lies in the fact that each dipole is constituted by a cylindrical conductive element and the linear conductor placed on the axis of said cylinder. This leads to a configuration in which the physical length of the cylindrical element does not correspond to its radiating length. The antenna is thus not properly tuned to its working frequency.